1. Field of the Invention
The present invention relates to microphone devices, and in particular, to silicon microphone packages.
2. Description of the Related Art
Ever since silicon microphones have been mass produced for mobile phones in 2003, microphones based on silicon semiconductor technology have been subjected to increasingly extensive research. Accordingly, annually, silicon microphones are increasing market share when compared to conventional electret condenser microphones (ECMs).
Compared to ECMs, a major advantage of silicon microphones is robustness against high temperatures and humidity. For a silicon microphone, such as a condenser silicon microphone, a microphone capacitor formed by a flexible membrane and a rigid back plate is charged by a constant potential supplied by an integrated ASIC (application-specific integrated circuit). Meanwhile, due to the ability of silicon microphones to undergo standard lead-free reflow soldering temperatures of up to 260° C., fully automated surface mount production lines may be used to manufacture silicon microphones. Accordingly, silicon microphones may be manufactured more reliably and cost less than ECMs.
Following are several disclosures concerning packaging of a silicon microphone.
U.S. Pat. No. 6,781,231 describes a microelectromechanical system package including a microelectromechanical system microphone, a substrate, and a cover. The substrate has a surface for supporting the microelectromechanical microphone. The cover includes a conductive layer having a center portion bounded by a peripheral edge portion. A housing is formed by connecting the peripheral edge portion of the cover to the substrate. The center portion of the cover is spaced apart from the surface of the substrate to accommodate the microelectromechanical system microphone. The housing includes an acoustic port to allow an acoustic signal to reach the microelectromechanical system microphone.
U.S. Pat. No. 7,434,305 describes a silicon condenser microphone package comprising a transducer unit, a substrate, and a cover. The substrate includes an upper surface having a recess formed therein. The transducer unit is attached to the upper surface of the substrate and overlaps at least a portion of the recess wherein a back volume of the transducer unit is formed between the transducer unit and the substrate. The cover is placed over the transducer unit and includes an aperture.
U.S. Pat. No. 7,439,616 discloses a silicon condenser microphone package including a transducer unit, a substrate, and a cover. The substrate includes an upper surface transducer unit, which is attached to the upper surface of the substrate and overlaps with at least a portion of the recess, wherein a back volume of the transducer unit is formed between the transducer unit and the substrate. The cover is placed over the transducer unit and either the cover or the substrate includes an aperture.
U.S. Pat. No. 7,447,323 relates to a surface mountable acoustic transducer system, comprising one or more transducers, a processing circuit electrically connected to the one or more transducers, and contact points arranged on an exterior surface part of the transducer system. The contact points are adapted to establish electrical connections between the transducer system and an external substrate. The contact points are further adapted to facilitate mounting of the transducer system on the external substrate by conventional surface mounting techniques.
U.S. Pat. Publication No. 2007/0071260 discloses a silicon-based transducer assembly coupled to a movable structure in a hearing instrument. The transducer assembly includes at least one microphone chip and an ASIC having multiple integrated components such as any combination of a DSP, an A/D converter, an amplifier, a filter, or a wireless interface. The movable structure may be a battery access door, a volume dial, a switch, or a touch pad. A protection strip can be disposed across the battery access door to prevent debris from clogging the silicon-based transducer assembly. The transducer assembly may also include an array of microphone chips to achieve adaptive beam steering or directionality. When equipped with a wireless interface, the hearing instrument wirelessly communicates with another hearing instrument or with a network.
The packaging schemes disclosed in the above U.S. patents and patent application publications provide silicon microphone packages that allow acoustic energy to contact a transducer disposed within a housing. The housing provides necessary pressure reference while at the same time protects the transducer from light, electromagnetic interference and physical damage. In principle, the packaging schemes disclosed in the above U.S. patents and patent application publications use a system-in-package method. In other words, the packaging schemes typically package two chips, that is, one silicon sensing chip and one ASIC chip in a cavity, to form the entire microphone package. To reduce negative parasitic effects, the above disclosed packaging schemes require wire bonding between the silicon sensing element and ASIC and/or the PCB substrate that supports both of those chips.
Since the silicon microphone packages formed by the system-in-package method require mounting of the silicon sensing chip and the ASIC chip onto a package substrate, wire bonding is needed to form electrical connections therebetween. The silicon microphone packages formed by the system-in-package method thus encompass both the silicon sensing chip and the ASIC chip, which hinders further miniaturization of silicon microphones.